In an internal combustion engine of an automobile, an oil-passage structure is provided. The internal combustion engine is constructed such that a crankshaft is supported by the cylinder block and a plurality of auxiliaries or auxiliary devices are provided; a crank pulley and a crank timing sprocket are provided on the crankshaft; camshafts for opening and closing an intake valve and an exhaust valve, respectively, are supported on a cylinder head; cam sprockets are provided on the camshafts; a timing chain is wound around the crank timing sprocket and the cam sprockets; a chain cover extending over the cylinder block and the cylinder head is provided so as to cover the timing chain; a driving belt is wound around each of the auxiliaries and around the crank pulley; an oil pump to be driven by the crankshaft is provided; and an oil control valve for operating a hydraulic actuator of a variable valve timing system is provided to thereby introduce oil from the oil pump to the oil control valve.
The variable valve timing system is constructed as shown in FIG. 11: the oil pump 204 and the crank timing sprocket 206 are provided on the crankshaft 202; the intake and exhaust cam sprockets 212 and 214 are provided on the intake and exhaust camshafts 208 and 210, respectively; the timing chain 216 is wound around the crank timing sprocket 206 and the intake and exhaust cam sprockets 212 and 214; the hydraulic actuator 218 as a hydraulic unit is provided at one end of the intake camshaft 208; the oil control valve 220 for operating the hydraulic actuator 218 is provided on a cylinder head (not shown) and control means such as an electronic control unit (ECU) 222 (shown schematically) for operating the oil control valve 220 is provided. The control means 222 communicates with a crank angle sensor 224 and a cam angle sensor 226 via electrical signals (shown in dotted lines on FIG. 11) whereby the optimum valve timing is calculated according to the operating condition of the internal combustion engine. The oil pressure (depicted by the solid line in FIG. 11) supplied to the hydraulic actuator 218 is controlled by operating the oil control valve 220 to vary the phases of the intake cam shaft 208 and the crankshaft 202.
In the above case, as shown in FIG. 12, in order to introduce the oil from the oil pump 204 on the side of the cylinder block to the oil control valve 220 on the side of the cylinder head, a pipe connection 230 at one end of the oil pipe 228 is fixed to the cylinder block 234 by means of a union bolt 232 and a pipe connection 236 at the other end of the oil pipe 228 is fixed to an intake cam cap 240 (for retaining the intake camshaft 208) by means of an additional union bolt 238.
Examples of such an oil-passage structure are disclosed in Japanese Patent Laid-Open Nos. 8987/1998, 8988/1998, 170415/1997, 170416/1997 and 212918/1994. The structure described in Japanese Patent Laid-Open No. 8987/1998 is such that the entire chain cover is formed by a material different from that of the cylinder head and a portion to which the oil supply portion of the variable valve timing system is fixed is formed integrally with the chain cover, thereby improving the assembly operation. The structure described in Japanese Patent Laid-Open No. 8988/1998 is the same as that which is disclosed in Japanese Patent Laid-Open No. 8987/1998 in that first and second camshafts are provided, a variable valve timing unit is provided on the second camshaft, and the oil housing main body of the second camshaft is arranged outside with respect to the primary sprocket of the first camshaft to thereby make the structure compact. Further, the structure described in Japanese Patent Laid-Open No. 170416/1997 is the same as that which is disclosed in Japanese Patent Laid-Open No. 170415/1998 in that a controlling oil passage and a lubricating oil passage are arranged forward and rearward, respectively, across the engine thereby making the structure compact. Lastly, the structure described in Japanese Patent Laid-Open No. 212918/1994 is such that in the case of the variable valve timing system of a V-type engine, an operating oil pressure path connecting an oil pressure control valve and a variable control mechanism is provided by making use of the space between the right and left banks of the engine.
Now, in the case of the conventional internal combustion engine provided with a variable valve timing unit, an oil passage is formed in the chain cover so as to establish an oil passage system for introducing oil from the main gallery formed in the cylinder block to the oil control valve and an oil passage communicating with the above-described oil passage is formed by drilling a hole through the tensioner bracket, whereby the belt tensioner and the tensioner bracket are arranged close to the cylinder block. However, the formation of the oil passage by drilling a hole through the tensioner bracket has created difficulties or inconveniences in that in situations where the tensioner bracket is required to be moved due to restrictions in the layout for each vehicle type, the tensioner bracket cannot be arranged at the proper position. Thus the number of processing steps increases which results in increases in the equipment and processing costs. Further, the temperature of the oil increases due to the heat of the internal combustion engine which has a negative effect on the functioning of the oil control valve.
In addition, in the case where an oil pipe is arranged outside the belt tensioner so as to overlap the latter for the purpose of establishing an oil passage system which introduces oil from the main gallery formed in the cylinder block to the oil control valve, there have hitherto been such inconveniences that when the internal combustion engine is mounted in the vehicle body, the oil pipe tends to come into contact with the vehicle body resulting in possible damage to the oil pipe. Further, since the oil pipe is arranged astride the driving belt for the auxiliaries, when the belt is replaced, it becomes necessary to remove the oil pipe thereby increasing service time.
Therefore, in order to eliminate or at least minimize the above-described inconveniences, the present invention includes: an oil-passage structure of an internal combustion engine having a cylinder block provided with a plurality of auxiliaries or auxiliary devices; a crankshaft provided with a crank pulley and a crank timing sprocket and supported by the cylinder block; a cylinder head positioned on the cylinder block; camshafts supported by the cylinder head for opening and closing intake valve and exhaust valves; cam sprockets attached to the camshafts; a timing chain wound around the crank timing sprocket and the cam sprocket; a chain cover extending over the cylinder block and the cylinder head so as to cover the timing chain; a driving belt wound around pulleys for a plurality of auxiliaries and around the crank pulley; an oil pump to be driven by the crankshaft; an oil control valve for operating hydraulic equipment whereby oil from the oil pump is introduced to the oil control valve; and an external oil pipe connecting the oil pump and the oil control valve and arranged between the auxiliaries driving belt and the chain cover.
According to the present invention, since an external oil pipe is provided between the auxiliaries driving belt and the chain cover so as to connect the oil pump and the oil control valve, it is no longer necessary to drill an oil passage hole in the tensioner bracket as has conventionally been necessary, and the tensioner bracket can be moved to a proper position when necessary due to restrictions in layout for each vehicle type. Further, it is also possible to reduce equipment processing costs by reducing the number of processing steps, and it is also possible to maintain proper functioning of the oil control valve by cooling the oil supplied to the oil control valve.
Further, since the oil pipe does not project outwardly, the oil pipe does not come into contact with the body of the vehicle at the time of mounting the internal combustion engine, thereby preventing possible damage to the oil pipe. Further, when the auxiliaries driving belt is replaced, it is not necessary to remove the oil pipe thereby improving serviceability.